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What Dave said about filling out your Fun Pass is really important to be done ahead of embarkation day. It will make things so much smoother and faster for you at check-in.
You don't have to go "over-board" for formal night. Business casual for guys will fly, ie Dockers and a nice shirt, preferably with a tie, but will work without.
I swore I would never touch this formal night jeans issue again. I will say after a heated discussion a long time ago with Dave on this subject I reached this conclusion:
If you are from Texas, and wear your best new jeans that is considered Formal for a cruise from that region.
Most folks, not all apparently, consider it very tacky and disrespectful of the occasion. They sorta call it Formal night for a reason.
Point being, you don't have to have a dress or tux, or even a suit. Just wear something nice. As you don't want to miss this dinner